iPad 2 digital av adapter not full screen on HDTV

I just got the iPad 2 and the Apple Digital AV Adapter. Plug it in Sharp 46" LED TV and everything seems fine, but the problem is that the screen display isn't full screen. The scree size appears to about 1/4 of my TV screen.The iPad resolution is lower than the TV res, so you have to set your TV resolution to 720p or automatic. A few HDMI TVs support to zoom the image to fill the screen top to